1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for exposing stimulable phosphor sheets to a radiation passing through an object to have a radiation image of the object stored thereon, exposing the respective stimulable phosphor sheets to stimulating rays which cause them to emit light in proportion to the stored radiation energy, and detecting and converting the emitted light into electric signals. This invention particularly relates to a radiation image recording and read-out apparatus wherein the stimulable phosphor sheets are circulated by a circulation and conveyance means along a predetermined circulation path and reused for radiation image recording.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet or simply as a sheet) is first exposed to a radiation passing through an object to have a radiation image stored thereon, and is then scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted by the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted into an electric image signal, which is processed as desired to reproduce a visible image having an improved image quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, in a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for use in the aforesaid radiation image recording and reproducing system and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load the mobile X-ray diagnostic station with a large number of stimulable phosphor sheets, and the number of the stimulable phosphor sheets which can be loaded on the mobile X-ray diagnostic station is limited. Therefore, it is desired to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, temporarily store the radiation images of the objects on the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets to a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examination. This is very advantageous in practical use.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored thereon should be erased by using a method as described, for example, in U.S. Pat. No. 4,400,619 or Japanese Unexamined Patent Publication No. 56(1981)-12599. The stimulable phosphor sheet may then be used again for radiation image recording.
From the aforesaid viewpoint, the applicant proposed in Japanese Unexamined Patent Publication No. 59(1984)-192240 a built-in type radiation image recording and read-out apparatus comprising:
(i) a circulation and conveyance means for conveying at least one stimulable phosphor sheet for recording a radiation image thereon along a predetermined circulation path,
(ii) an image recording section positioned on said circulation path for recording a radiation image of an object on said stimulable phosphor sheet by exposing said stimulable phosphor sheet to a radiation passing through said object,
(iii) an image read-out section positioned on said circulation path and provided with a stimulating ray source for emitting stimulating rays for scanning said stimulable phosphor sheet carrying said radiation image stored thereon at said image recording section, and a photoelectric read-out means for detecting light emitted by said stimulable phosphor sheet scanned with said stimulating rays to obtain an electric image signal, and
(iv) an erasing section positioned on said circulation path for, prior to the next image recording on said stimulable phosphor sheet for which the image read-out has been conducted at said image read-out section, having said stimulable phosphor sheet release the radiation energy remaining on said stimulable phosphor sheet, whereby said stimulable phosphor sheet is circulated through said image recording section, said image read-out section and said erasing section and reused for radiation image recording.
Since the built-in type radiation image recording and read-out apparatus is one that can be very conveniently used for, for example, mounting on a mobile X-ray diagnostic station as mentioned above, it is desirable that the apparatus can conduct continuous image recording and read-out operations at as short intervals as possible and is small.
On the other hand, in the aforesaid built-in type radiation image recording and read-out apparatus, stimulable phosphor sheets are circulated through the image recording, image read-out and erasing steps. When image recording is conducted continuously as mentioned above, it is necessary that a plurality of stimulable phosphor sheets readied for image recording by erasing be fed continuously to the image recording section. However, the time required for the image read-out step and the time required for the erasing step are longer than the time required for the image recording step, among which the time required for the image read-out step is the longest (for example, approximately 45 seconds). Therefore, in the case where image recording is conducted each time the stimulable phosphor sheet on which image read-out and erasing are finished is returned to the image recording section, a problem that arises is that the image recording interval becomes long. Accordingly, when image recording is conducted continuously, it is necessary to provide the circulation path between the erasing section and the image recording section with a waiting zone for keeping waiting a plurality of erased stimulable phosphor sheets, from which the sheets may be taken out one by one. On the other hand, though the stimulable phosphor sheets subjected to image recording must be sequentially sent to the image read-out section for conducting image read-out therefrom, the image read-out time is very much longer than the image recording time, and the second and subsequent sheets on which image recording is finished cannot immediately be conveyed to the image read-out section. Therefore, it is also necessary to provide the circulation path between the image recording section and the image read-out section with a waiting zone for keeping waiting a plurality of stimulable phosphor sheets carrying a radiation image stored thereon, from which the sheets may be taken out one by one each time the image readout section is readied for the read-out operation. The waiting zone is proposed in, for example, Japanese Patent Application Nos. 59(1984)-112377 and 59(1984)-112378. Consequently, in order to conduct image recording continuously with the built-in type radiation image recording and read-out apparatus, it is necessary to dispose two waiting zones, one prior to the image recording section and the other after the image recording section. Thus the apparatus becomes large, its configuration becomes complicated, and its manufacturing cost becomes high.